Earth's poles precess over a 26, year period and therefore the constellations aligned along the Sun''s path, called the ecliptic, shift stations slowly over time, by about one degree every 73 years.
The dates the astrologers associate with the zodiac were valid about 2, years ago. For instance, the Sun was once in Aries on the first day of Spring. Now, it is in Pisces.
For this reason, curiously, astronomers still refer to the first day of Spring Vernal Equinox as the "First Point of Aries. Fall at the University of Southern Maine. Why can I be a Virgo, but not a Lupus? A Gemini but not a Lyra? Today's Hours November 11, When we look up from the surface of our planet, though, that's not what we see. We see constellations: two-dimensional pictures and shapes connecting stars in the sky to stories from cultures around the globe.
Those constellations are connected to myth and legend, as well as the unscientific concepts of modern astrology. But they were also important instruments that once marked the passage of time and the seasons.
Today, constellations continue to be valuable tools to orient astronomers and stargazers in the night sky. As Earth rotates , the sun, moon and planets seem to move generally along a set path through the sky, called the ecliptic.
The 13 constellations in the path of the ecliptic are:. Astrologers use 12 of these constellations to roughly correspond with the signs of the zodiac to make predictions. They omit Ophiuchus , because when the signs were first described the stars were not in exactly the same position as they are today.
Today, the astrological signs differ from constellations, bearing only a loose reference to one another. The sign of Pisces, for instance, currently corresponds to the rise of the constellation of Aquarius. Read more: How the constellations got their names. From Earth, stars appear to move across the sky on a regular schedule. That appearance of star movement actually has more to do with the rotation of Earth than the movements of stars themselves.
Similar to how our sun looks like it's moving across the sky when it's really our planet rotating as it orbits the sun, constellations appear to be moving when it's really our viewpoint that is changing. So, what we actually see from any given spot on Earth only looks like a rotating collection of constellations. Read more: Space junk is blocking our view of the stars.
The Moon and the Sun exert a gravitational drag on the Earth's equatorial bulge, trying to pull the Earth's equatorial region to be aligned with the ecliptic plane.
This pull, along with the rotational motion of the Earth on its axis, the revolution of the Earth around the Sun, and the revolution of the Moon about the Earth, cause the Earth to wobble about its axis of rotation, similar to the motion of a spinning top.
This motion is called precession. It is the wobbling of the equatorial plane that causes the line of the intersection of the equatorial and ecliptic planes to move. As mentioned above, the intersection of these two planes determine where on the zodiac our spring and fall equinoxes occur. This line of intersection is said to precess or move around the zodiac because of the wobble.
Figure 5 Circular path that the north equatorial pole describes due to the precession of the Earth. Figure 4 shows a schematic of the Earth's precession, this effect gradually changes where on the zodiac the equinox points fall. This precession means that the spring equinox was just entering Pisces years ago and it is about to enter the constellation of Aquarius that is the reason why many astrologers say that we are going to start the Aquarius epoch. An extension of the Earth's axis out into space traces out a conical figure with a time cycle or period of 26, years.
The Earth's precession implies that although Polaris is currently the star above our north pole, in about 13, years Vega will become our north star; only after yet another 13, years, will the north pole will once again point towards Polaris, as shown in Figure 5.
Therefore, because of the Earth's precession, the constellation which is behind the Sun nowadays is actually different from the one predicted by astrologers. Ophiuchus, the 13 th constellation of the zodiac. The constellations of the zodiac at the present. Unlike the zodiac signs in astrology, the astronomical constellations vary widely in size. If we think of the sky as a great sphere, the areas that different constellations cover can be drawn fairly accurately.
There are a number of days of the Earth's orbit when the Sun is between our planet and any one of the zodiacal constellations. Since each constellation is of different size and since the ecliptic passes through larger or smaller portions of each constellation, and the speed of the Earth around the Sun varies along its orbit, the Sun is between the Earth and each zodiacal constellation for varying periods.
For example, more days 44 days are spent with the Sun between the Earth and the largest constellation, Virgo, than are spent with the Sun between the Earth and the smallest constellation, Scorpius 7 days. This was essentially a mapping exercise to make the work of astronomers more efficient.
At present our ecliptic passes through the boundaries of 13 constellations, the usual 12 and a new one known as Ophiuchus or Serpentarius.
Ophiuchus is depicted as a man supporting a serpent, the interposition of his body divides the snake into two parts, Serpens Caput and Serpens Cauda. Ophiuchus, is located in a position near the center of the Milky Way galaxy amid clouds of molecular hydrogen and dust. In addition, although not part of the original constellation stars, the so-called Barnard's Star is located within Ophiuchus; this object has the largest known proper motion relative to the Sun. Just as a remark, within a few hundred years the ecliptic will no longer pass through Scorpius but will also include the constellation of Orion.
Most astrologers use a different system to determine the size of our zodiacal constellations. This point occurred years ago in the constellation of Aries, but nowadays this occurs in the constellation of Piscis, making this constellation the start-point of the current zodiac solar system.
The following table provides the dates at which the Sun is located within the boundaries of a specific zodiac constellation as defined in by the International Astronomical Union, i.
The dates can vary by as much as 2 days from year to year, depending on the cycle of leap years.
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